Page 997 - The Toxicology of Fishes

Estrogenic Effects of Treated Sewage Effluent on Fish in English Rivers 977

A B

C D

E F

FIGURE 25.4 Histological sections showing the presence of oocytes in the testis of intersex roach (Rutilus rutilus). (A)
Normal ovary; (B) normal testis; (C, D) mildly intersex gonad with both testicular germ cells and a few primary oocytes;
(E, F) severely intersex gonad, with testicular germ cells and large numbers of both primary and secondary oocytes. Tl,
testis lobule; Po, primary oocyte; So, secondary oocyte; Zr, zona radiata; n, nucleus. Scale bar represents 100 µm.

the upstream population to the one downstream may have occurred during periods of spate. Most of the
reference sites were still waters (lakes and canals) because it proved extremely difficult to find rivers in
the United Kingdom that contained healthy populations of roach but that did not receive effluent from
sewage treatment works. Histological examination of the gonads revealed that a large proportion of the
putative males were in fact intersex, as defined by the simultaneous presence of both testicular and
ovarian characteristics (oocytes and/or an ovarian cavity) in the gonads. Intersex fish were found at all
sites, but the incidence was considerably lower at the control sites (from 4% in the laboratory fish up
to 18% at one field site) compared to that of populations of roach in rivers downstream of STW outfalls,
where the proportion of intersex males ranged from 16% (River Wreake/Eye) to 100% (in both the River
Aire in Yorkshire and the River Nene in Northamptonshire) (Jobling et al., 1998). In contrast, the
incidence of intersexuality in roach at the upstream sites ranged from 11.7% (River Lea) up to 44.4%
(River Nene), values that were typically lower than their respective downstream sites (Figure 25.6).
More recently, a considerably wider survey of roach living in U.K. rivers was carried out to further
investigate for sexual disruption wild populations. In this work, 1615 roach were sampled from 51 river
sites and feminization of the gonad and reproductive duct was found at 44 of those sites (86% of those
studied) (Jobling et al., 2005). A more limited survey of juvenile roach living in 7 U.K. rivers with
varying water quality found that the majority of roach from 5 of these rivers had female-like ducts
(Beresford et al., 2004). The effects reported in wild fish in these English rivers are not limited to roach.